Researchers at Texas Tech and Yale Explain How to Make the Hardest Metal Pliable

Researchers have discovered a way to predict and control the properties of metallic
glasses, yielding a highly versatile material that looks like metal, is moldable like
plastic, but stronger than steel.

Researchers at Texas Tech University and Yale University have discovered a way to
predict and control the properties of metallic glasses, yielding a highly versatile
material that looks like metal, is moldable like plastic, but stronger than steel.

The study, “Critical fictive temperature for plasticity in metallic glasses,” is published
in the journal Nature Communications and reveals that there is a critical fictive
temperature to obtain a glassy state capable of plastic deformation. The study shows
there is a critical cooling rate, based on the critical fictive temperature, for pliability
in metallic glasses. If the glass is cooled more slowly than the critical cooling
rate, it will be brittle.

Golden Kumar, assistant professor of mechanical engineering at Texas Tech, and Jan
Schroers, professor of mechanical engineering and materials science at Yale University,
have developed a model that can explain why some metallic glasses are always ductile
or brittle, whereas others are sensitive to processing and aging. The model is based
on the metallic glass’ fictive temperature.

Metallic glasses are unique because they combine traits of metals, plastics and glasses
in one material. These materials conduct heat and electricity like metals, but their
glassy structure makes them moldable like plastics, but hard like glasses. In the
process of creating these metallic glasses, it has been difficult to predict the exact
properties of the end product, as the materials can be ductile or brittle depending
on their composition, sample size and preparation conditions. Despite numerous efforts
in the past, no single theory could explain the effect of all of these factors on
the properties of metallic glasses.

“By comparing the critical fictive temperature values for different metallic glasses,
we can now tell which one will be ductile or brittle under typical conditions,” Kumar
said. “This can explain why some metallic glasses were always brittle; their critical
fictive temperature is beyond experimentally accessible fictive temperature.”

Metallic glasses typically contain four or five elements, such as zirconium, titanium,
copper, nickel, aluminum, platinum, iron and others. However, it is the main element
that determines the cost and application. Zirconium-based metallic glasses, for example,
exhibit high strength and elasticity, and may be used in sporting goods or military
applications, while titanium-based metallic glasses may be considered for precision
medical tools because of their biocompatibility.

“The model will help to develop an alloy-specific preparation recipe for obtaining
plasticity in metallic glasses,” Schroers said. “This is a crucial step toward predictive
models for plastic deformation of metallic glasses.”

Other co-authors who contributed to the study are Pascal Neibecker and Yanhui Liu
at Yale.